This invention relates to a wire saw device for cutting a brittle material, and more particularly to a method of preventing a machining solution from staying and sticking at the machined part of a workpiece, and a method of preventing a machining solution from being deteriorated in machining capacity.
One example of a conventional method of cutting a brittle material such as semiconductor materials, magnetic materials, ceramics and glass is as follows: A wire and a brittle material to be machined (hereinafter referred to as "a workpiece", when applicable) are abutted against each other with a machining solution interposed therebetween, and, under this condition, while they are reciprocated relative to each other, the brittle material is lapped with abrasive grains in the machining solution.
In the conventional method, the wire is pushed by the workpiece from below. As shown in FIG. 1, a wire 1 is wound over a plurality of grooved rollers 2 (for instance three rollers) several turns with a predetermined pitch, and the wire 1 thus laid is reciprocated straightly while the workpiece 3 is pushed against the wire 1. In this operation, a plurality of nozzles 4 held above the workpiece 3 jet a machining solution 5 to the workpiece 3, so that the latter 3 is cut by the abrasive grains in the machining solution 5.
In the method, as shown in FIG. 2, a wedge-shaped space 10 is formed between the wire 1 and the workpiece 3 downstream of the wire 1 as viewed in the direction of movement of the wire 1. The wedge-shaped space 10 is located below the wire 1, and therefore it is rather difficult for the machining solution 5 to go into the space 10. On the other hand, the abrasive grains may stay in and stick to the gaps between the machined parts of the workpiece 3, and the thin plates formed may incline. As a result, when the workpiece 3 is disengaged from the wire 1 after machined, the machined surface may be scratched or cracked by the wire 1. In order to overcome this difficulty, the workpiece 3 machined is washed with cleaning oil for a long period of time; however, it is impossible to completely remove the abrasive grains from the gaps, and therefore it is impossible to completely prevent the machined surfaces from being scratched or cracked. In the washing operation, the cleaning solution is mixed with the machining solution 5, thus reducing the service life of the latter 5.
In view of the foregoing, in order to positively supply the machining solution 5 to a cutting part of the workpiece, a method of machining a workpiece in a machining-solution supplying vessel 6 as shown in FIG. 3 has been proposed in the art. In the method, the machining solution 5 is sufficiently supplied to the cutting part of the workpiece, thus preventing the abrasive grains from staying in and sticking to the gaps between the machined parts of the workpiece. However, the method is still disadvantageous in that it is rather troublesome to lay the wire 1 over the rollers and to set the workpiece 3 at the machining position, and the thin plates formed by cutting are liable to incline, and the inclination of the thin plates cannot be positively prevented.
U.S. Pat. No. 4,655,191 to Wells et al has disclosed a method of cutting a workpiece with a wire from below. In the method, the machining solution will flows sufficiently into the wedge-shaped space. However, the method is also disadvantageous in the following point: The gaps formed in the workpiece by machining provide passages for the machining solution; that is, the gaps are not positively immersed in the machining solution pooled. Therefore, the abrasive grains are liable to stay in and stick to the gaps. Accordingly, in removing the wire from the workpiece, it may scratch or crack the machined surface.